Physical vapor deposition
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Physical vapor deposition (PVD), sometimes (especially in single-crystal growth contexts) called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings. PVD is characterized by a process in which the material goes from a condensed phase to a vapor phase and then back to a thin film condensed phase. The most common PVD processes are sputtering and evaporation. PVD is used in the manufacture of items which require thin films for mechanical, optical, chemical or electronic functions. Examples include semiconductor devices such as thin film solar panels, aluminized PET film for food packaging and balloons, and titanium nitride coated cutting tools for metalworking. Besides PVD tools for fabrication, special smaller tools (mainly for scientific purposes) have been developed.
The source material is unavoidably also deposited on most other surfaces interior to the vacuum chamber, including the fixturing used to hold the parts.
- Cathodic arc deposition: a high-power electric arc discharged at the target (source) material blasts away some into highly ionized vapor to be deposited onto the workpiece.
- Electron-beam physical vapor deposition: the material to be deposited is heated to a high vapor pressure by electron bombardment in "high" vacuum and is transported by diffusion to be deposited by condensation on the (cooler) workpiece.
- Evaporative deposition: the material to be deposited is heated to a high vapor pressure by electrical resistance heating in "high" vacuum.
- Close-space sublimation, the material, and substrate are placed close to one another and radiatively heated.
- Pulsed laser deposition: a high-power laser ablates material from the target into a vapor.
- Sputter deposition: a glow plasma discharge (usually localized around the "target" by a magnet) bombards the material sputtering some away as a vapor for subsequent deposition.
- Pulsed electron deposition: a highly energetic pulsed electron beam ablates material from the target generating a plasma stream under nonequilibrium conditions.
- Sublimation sandwich method: used for creating man-made crystals.
Various thin film characterization techniques can be used to measure the physical properties of PVD coatings, such as:
- Calo tester: coating thickness test
- Nanoindentation: hardness test for thin-film coatings
- Pin-on-disc tester: wear and friction coefficient test
- Scratch tester: coating adhesion test
- X-ray micro-analyzer: investigation of structural features and heterogeneity of elemental composition for the growth surfaces 
Comparison to other deposition techniques
- PVD coatings are sometimes harder and more corrosion-resistant than coatings applied by the electroplating process. Most coatings have high temperature and good impact strength, excellent abrasion resistance and are so durable that protective topcoats are rarely necessary.
- Ability to utilize virtually any type of inorganic and some organic coating materials on an equally diverse group of substrates and surfaces using a wide variety of finishes.
- More environmentally friendly than traditional coating processes such as electroplating and painting.
- More than one technique can be used to deposit a given film.
- Specific technologies can impose constraints; for example, the line-of-sight transfer is typical of most PVD coating techniques, however, some methods allow full coverage of complex geometries.
- Some PVD technologies typically operate at very high temperatures and vacuums, requiring special attention by operating personnel.
- Requires a cooling water system to dissipate large heat loads.
Application: Anisotropic Glasses
PVD can be used as an application to make anisotropic glasses of low molecular weight for organic semiconductors. To understand what the properties of this glass are that make it useful, first a brief idea of the mechanism. The parameter needed to allow the formation of this type of glass is molecular mobility and anisotropic structure at the free surface of the glass. The configuration of the polymer is important where it needs to be positioned in a lower energy state before the added molecules bury the material through a deposition. This process of adding molecules to the structure starts to equilibrate and gain mass and bulk out to have more kinetic stability. The packing of molecules here through PVD is face-on, meaning not at the long tail end, allows further overlap of pi orbitals as well which also increases the stability of added molecules and the bonds. The orientation of these added materials is dependent mainly on temperature for when molecules will be deposited or extracted from the molecule. The equilibration of the molecules is what provides the glass with its anisotropic characteristics. The anisotropy of these glasses is valuable in it allows a higher charge carrier mobility and the higher the density of the glass the increase of charge transfer as well. This process of packing in glass in an anisotropic way is valuable due to its versatility and the fact that glass provides added benefits beyond crystals, such as homogeneity and flexibility of composition.
By varying the gases and duration of the process, a range of colors is produced by Physical Vapor Deposition on stainless steel. The resulting colored stainless steel product can appear as brass, bronze, and other metals or alloys. This PVD-colored stainless steel can be used as exterior cladding for buildings and structures, such as the Vessel sculpture in New York City and The Bund in Shanghai. It is also used for interior hardware, paneling, and fixtures, and is even used on some consumer electronics, like the Space Gray and Gold finishes of the iPhone X, XS, and 11 Pro.
As mentioned previously, PVD coatings are generally used to improve hardness, wear-resistance, and oxidation PVD-colored Thus, such coatings are used in a wide range of applications such as:
- Architectural ironmongery, panels, and sheet
- Dyes and molds for all manner of material processing
- Cutting tools
- Thin-films (window tint, food packaging, etc.
- Metals (aluminum, copper, bronze, etc.)
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